This invention is related to a magnetic recording medium, a method for manufacturing the same, and a magnetic recording apparatus.
In recent years, with higher computer utilization, the quantity of data handled in computer systems has risen rapidly, and there has been a corresponding increase in the need for high-speed data exchange. A magnetic rigid disk recording system has recently been put to practical use as an external storage device to meet this need.
In the magnetic rigid disk recording system, transducer heads fly above the recording surface of a rotating disk-shaped magnetic recording medium, reading or writing data to the medium. By reducing the flying height, higher-density data can be recorded. To keep this very low height stable, a contact start/stop (CSS) method is used, in which the head is in contact with the disk surface when it is at rest. Employment of this method has greatly contributed to an increase in the recording density, but at the same time has caused various new problems. One of these problems is strong adhesion between the head and the disk when they are at rest.
In order to solve this problem, a method called texturing has been employed for mechanically making the disk substrate surface uneven by using abrasive particles. The roughness of the substrate surface is reflected in the surface roughness of a disk completed by depositing magnetic layers and so on, and accordingly tile static friction coefficient between head and disk decreases, and this in turn reduces the adhesion force. However, this method easily causes irregularities in the disk surface roughness. As a consequence, problems arise when high asperity causes a head crash or when impure materials react chemically with magnetic layers in deep valleys. In addition, a process for texturing must be undertaken before disposing thin films on the substrate. Furthermore, the process requires large-scale apparatus, which increases the cost.
As a technique for solving this, it is proposed in the Japanese Published Unexamined Patent Application No. 46223/1989 (1-46223) official gazette that an uneven underlayer be formed by depositing grains of an inorganic compound such as SiO.sub.2 or a pure metal element such as Cu on the disk substrate by means of a sputtering method or evaporation method, and that a magnetic layer be provided thereon. However, this technique involves the problems of peeling of the underlayer from the substrate, degradation of magnetic properties, and insufficient surface roughness for texturing, and thus it is not suitable for practical use.
Further, as disclosed in the Japanese Published Unexamined Patent Application No. 240429/1986 (61-240429) official gazette, an attempt was made to improve the magnetic properties of the magnetic layer by applying an underlayer of a metal with a low melting point. The metals of this type disclosed therein are In, Sn, Bi, Ga, and Gain. However, this attempt did not positively utilize deposition of such a metal onto a substrate as an alternative to mechanical texturing. There was also a problem of marked degradation of the magnetic properties of the magnetic layer. The coercive force of the medium disclosed in this official gazette has a very low value of 600 Oe.
In the Japanese Published Unexamined Patent Application No. 189922/1991 (3-189922) official gazette, deposition of a low-melting-point metal underlayer is used as an alternative to mechanical texturing. The method disclosed therein comprises the steps of depositing a transient liquid metal on a substrate, and maintaining the liquid metal layer in a liquid state while depositing a magnetic layer on the transient liquid metal layer, whereby the transient liquid metal reacts with the magnetic layer. The material of the underlayer that is the main subject of discussion is a pure metal (Ga). However, although the maximum coercive force of the medium shown as an embodiment is about 1800 Oe, its coercive squareness remains about 0.6. Accordingly, it can be said that there is room for improvement in its magnetic properties. Further improvement is also desired in the roughness of the medium surface. It is explained later that, if the above method is used, the underlayer must be made thick to obtain a surface roughness of substantially the same degree as in the present invention.